C 203 1 



imbibed by aquatic plants, or be deposited in fome 

 other manner. 



Having found, by feveral experiments above- 

 mentioned, that the proper putrid effluvium is fome- 

 thing quite diftinct from fixed air, and rinding, by 

 the experiments of Dr. Macbride, that fixed air cor- 

 reels putrefaction ; I once concluded that this effect 

 was produced, not by flopping the flight of the fixed 

 air, or reftoring to the putrefying iubftance the 

 very fame thing that had efcaped from it; and 

 which was the common vinculum of all its parts 

 (which is that ingenious author's hypothecs) but 

 by an affinity between the fixed air and the putrid 

 effluvium. It therefore occurred to me, that fixed 

 air, and air tainted with putrefaction, though 

 equally noxious when feparate, might make a 

 wholefome mixture, the one correcting the other ; 

 and I was confirmed in this opinion by, I believe, 

 not iefs than fifty or fixty inftances, in which air,, 

 that had been made in the higheft degree noxious, 

 by refpiration or putrefaction, was fo far fweetened, 

 by a mixture of about four times as much fixed air 

 that afterwards mice lived in it exceedingly well,- 

 and in fame cafes almofl as long as in common air. 

 I found it, indeed, to be more difficult to reftore 

 old putrid air by this means ; but I hardly ever 

 failed to do it, when the two kinds of air had ftood 

 a long time together, by which I mean about a; 

 fortnight or three weeks. 



The reafbn why I do not abfolutely conclude • 



that the reftoration of air in thefe cafes was the. 



effect of fixed air, is that, when I made a trial of 



the mixture, I fometimes agitated the two kinds 



D d 2 of 



